In the mass production of the IC packages, especially for memory packages, the development of the advanced packaging technologies is to simplify packaging processes for IC chips operating in higher frequencies. One kind of the current packages for the DDR II DRAM or XDR DRAM may be called as Chip-On-Board (COB), Board-On-Chip (BOC), or window BGA where a chip is directly attached to a wiring substrate. The chip is electrically connected to the substrate by a plurality bonding wires passing through the slot on the substrate. Then, the chip, the bonding wires, and the substrate are encapsulated by an encapsulant. Finally, solder balls are placed under the bottom surface of the substrate for external terminals for the packages. Compared to the leadframe-based packages such as TSOP, there are no outer leads extended from the sides of the encapsulant so that the electrical conductive paths are much shorter and the package footprint is much smaller.
As shown in FIG. 1, a conventional COB package 100 primarily includes a substrate 110, a chip 120, a plurality of bonding wires 140, an encapsulant 150, and a plurality of solder balls 160. The manufacturing process of the COB package 100 is also shown in FIG. 2. In step 11, a substrate 110 is provided. The substrate 110 has a first surface 111, a second surface 112, and a slot 113 for the passing of the bonding wires 140 where the substrate 110 is a rigid printed circuit board. Then, in step 12, the active surface 121 of the chip 120 is attached to the first surface 111 of the substrate 110 by a die-attaching film 130 where a plurality of bonding pads 122 formed on the active surface 121 of the chip 120 are aligned within the slot 113. Then, in step 13, wire bonding is performed for electrical connection, the bonding pads 122 of the chip 120 are electrically connected to the inner pads of the traces 114 of the substrate 110 by a plurality of bonding wires 140 passing through the slot 113. Then, in step 14, the chip 120 and the bonding wires 140 are encapsulated by an encapsulant 150 by molding. Finally, in step 15, the solder balls 160 are placed on the ball pads connected with the traces 114 of the substrate 110 on the second surface 112 of the substrate 110. After singulation, the package 100 is manufactured, which can electrically connect to external printed circuit boards such as mother boards, communication boards, or memory modules by SMT. However, the lengths of the bonding wires are too long to be implemented in high-speed applications, moreover, the manufacturing process are too complicated. For the high-speed applications in the future, the packages need to be much thinner and much lighter.